Method of forming commutators



y 6, 1933. E, T. REARDGN 1,909,634

METHOD OF FORMING COMMUTATORS Filed July 8, 1.931

Patented May 16, 1933 UNITED STATES PATENT OFFICE EARL T. REARDON, OF ST. LOUIS, MISSOURI, ASSIGNOR TO WAGNER ELECTRIC CORPO- RATION, OF ST. LOUIS, MISSOURI, A CORPORATION OF DELAWARE METHOD OF FORMING COMMUT'A'IORS Application filed July 8, 1931.

It has been found that the inter-bar insulating strips of commutators should not extend flush with the working face of the commutator but should terminate an ap preciable distance back of such face so as to avoid the possibility of the insulation projecting beyond the faces of the bars, thus causing sparking or even interrupting the flow of current between the brushes and the commutator bars. Heretofore the difficulty has been overcome by under cutting the commutators,that is a portion of each interbar insulating strip adjacent the working face has been removed by a suitable tool, such as a saw or a file. This operation is, however, not only slow and expensive but unless skillfully done may result in injury to the working face of the commutator.

It is the object of my invention to provide a simple, effective and inexpensive method of producing commutators with relieved inter-bar insulation, thus avoiding the necessity of under cutting the insulation with its attendant expense and liability of injury to the completed article.

The accompanying drawing illustrates my method as applied to the manufacture of one one form of commutator. Figure 1 is a longitudinal section of one-half of a completed commutator; Figure 2 is a sectional view showing the manner in which the parts are assembled; Figure 3 is a fragmentary elevation showing the commutator face; and Figure 4- is an enlarged section taken on the line l4 of Figure 3.

For the purpose of illustration I have shown a commutator of the vertical or disc type, such as that used in repulsion starting, induction running single phase motors, but my method is applicable to other types of commutators. Referring first to Figure 1, where the commutator is shown as mounted on a rotor shaft 1, the commutator comprises a hub 2, commutator bars 3, inter-bar insulating strips 4, and an insulating bond 5 securing the parts together to form an integral structure. The material of the bond 5 enters dovetail recesses formed in the bars and strips which are similar in contour except that the strips are somewhat narrower Serial No. 549,410.

than the bars throughout the greater part of ring 7 is interposed between the hub and the bars. I

In assembly of the parts, an aligning plate 8 and a form 9 are used. The alternating bars and strips are first placed upon the plate around thebase of the form, the rim 7 placed over the form, and finally, the hub is positioned on the ring. The parts are now ready for the application of the binder 5 which is accomplished under pressure and heat by a die (not shown) in the usual manner. Before the binder is applied an annular backing sheet 10 is placed in the bottom of the dovetail groove. This sheet is made of paper or other insulating material, which is flexible to permit its bending when being inserted in the dovetail groove. The object of the backing strip is to prevent the material of'the bond, while in a plastic state and under pressure, from being forced between the base and the strips and so filling up the relieving slots which it is the object of this invention to produce.

When the bond has become set, the commutator is ready for use except that it is usually desirable to true its face. This is accomplished by removing a portion of the face, as indicated by the broken line AA in Figure 4, by a machining operation, such as turning or grinding. Such machining operation is liable to produce burrs on the edges of the bars, which burrs would result in short circuits. To prevent this I fill the relieving slot, before the machining operation, with a friable material 11, such as litharge, which accomplishes this purpose. After machining, the filling may be removed, as shown at the left hand side of Figure 3, or it may be allowed to remain in place as, due to its friable or brittle nature, it will soon fall out in the normal operation of the machine.

A commutator like that illustrated is preferably used in conjunction with a brush which is of such dimensions as not to project over the feet 6 but contacts with the relieved portion only of the face, as shown by dotted lines 12 (F1 re 1). 5 Having fu ly described my invention, what claim as new and desire to secure by Letters Pdentof the United States is:

1. The method of making a commutator havin segment insulating strips spaced 10 from e brush 'contactinggortion of its surface, which consists of so rmi'ng each insulating strip as to provide two spaced projections on one side thereof, said projections being adjacent op osite ends of the strip, 1 alternately assem ing the brush contacting heel of the commutator segments and the projections of the insulating strips against an aaligni surface, and applying securing means to connect the parts together. a 2. An assein 1y oi commutator elements ing commutator bars and inter-bar strips, the edges of said insulating strips adjacent the working faces of the bars being provided with projections at each u terminatingin alignment with said work- C:

hoes. n tedimony whereof, I hereunto aflix my signature, this 2nd day of July, 1931.

EARL T. REAR-DON. 

